Obviously I don't know exactly what you are testing with the shuttle, other than it is to do with the ring frame and I/O.
OnSemi has synthesised the P2 remainder for you. I presume this has gone far enough to be fairly sure its ok.
Might it be possible to add the P2 synthesis into the ring frame for the shuttle?
Would there be much expense to add it in (might OnSemi add the synthesis for free/cheap) so that a better test might be done?
I know you need access to some parts of the ring frame. Could those special pins be connected via a mux and a "test" pin, so that they would otherwise be connected to the P2 logic? If not, then just scarifice those P2 pins for the testing?
As for the ROM, its quite easy to just "initialise" a small program into Cog 0 that just gives a really basic uart load and run into that cog. No smarts at all.
This would give a number of usable P2 test chips, rather than just ring frames.
Your thoughts ????